The waste products of tanneries generally are scraps ranging in size from millimeters to several centimeters, including shavings, trimmings and so-called "green" crusts, which are discarded at various stages of the tanning process. These scraps may also include fatty subcutaneous animal tissue subjected to the chrome treatment. The disposal of the scraps creates ecological problems since their mere dumping tends to pollute the environment. Thus, the residual chromium is washed out by rain so as to leave an organic mass susceptible to decay with consequent contamination of water and air.